As one skilled in this art appreciates the microturbine has in the last few years become extremely useful for generating electricity. Typically, the microturbine comprises a compressor, combustor, turbine and a recuperator which serves to pre-heat the compressor discharge air prior to being injected into the combustor. The work produced by the turbine serves to rotate the armature of the electrical generator and an invertor converts the electrical current and controls its frequency. Details of the microturbine can be obtained by referring to co-pending patent application Ser. No. 09/934,640 filed on Aug. 22, 2001 by William R. Ryan entitled RECUPERATOR FOR USE WITH TURBINE/TURBO-ALTERNATOR, published and U.S. Pat. No. 6,314,717 granted to Teets et al on Nov. 13, 2001 entitled ELECTRICITY GENERATING SYSTEM HAVING AN ANNULAR COMBUSTOR both of which are commonly assigned to the assignee of this patent application, and both being incorporated by reference herein. Also, for more details of this invention reference should also be made to the microturbines manufactured by the assignee, Elliott Energy Systems, Inc., of Stuart, Fla. and, particularly of the types exemplified by Model Number TA-80.
In certain residential or commercial applications the microturbine can also be utilized for powering a boiler for obtaining hot water or powering a chiller that can be used in a refrigeration absorption system. A simple system for obtaining these objectives is illustrated in FIG. 1 where a boiler is connected to the discharge of the recuperator. The temperature of the engine working medium discharging from the recuperator is typically over 500 degrees Fahrenheit and obviously, this temperature can be utilized wherever heat is needed, given that the heat can be transported efficiently and economically. The simple boiler application will be described hereinbelow in connection with the details of this invention.
This invention contemplates that the microturbine system includes a microturbine engine, a recuperator, an electrical generator and a boiler as described in the immediate above paragraph. This invention augments the above-described simple microturbine/boiler system by incorporating a second boiler. The second boiler can be utilized for the purpose of obtaining hot water at a higher temperature that is available in the single boiler system or obtaining steam. In this system the second boiler is optionally preset so that both of the boilers are in continuously or alternatively is turned-off one of the boilers is rendered inoperative, i.e. all of the turbine exhaust flows into the recuperator and then to the first boiler and by-passes the second boiler. This invention also contemplates utilizing the water for cooling purposes of some of the systems components prior to the water flowing to the boiler.
Another aspect of this invention is the use of the by-pass system to boost the temperature of the waste heat when used as a heat transport medium so as to assure that the delta temperature between this medium and the water is sufficient whereby efficient heat transfer will be effectuated. As one skilled in this technology appreciates, as the efficiency of the microturbine engine increases, the temperature of the exhaust being emitted from the turbine of the microturbine engine becomes reduced. Hence, given the need for a particular delta temperature in the indirect heat exchange relationship occurs, and the temperature of the engine working medium waste is not sufficient in the boiler, the amount of engine working medium waste can be throttled to provide the necessary delta to achieve efficient heat transfer.
This invention should not be confused with the microturbine by-pass system described and claimed in U.S. patent application contemporaneously filed by Gregory Brian Dettmer entitled MICROTURBINE DIRECT FIRED ABSORPTION CHILLER, and assigned to a common assignee. This system utilizes the recuperator exhaust heat to power a direct fired absorption chiller which would otherwise be unacceptable without the provisions of the Dettmer invention. In the Dettmer patent application, supra, the system includes a by-pass system for the recuperator, and is uniquely designed to provide a predetermined constant temperature for the direct fired absorption chiller. As mentioned above this by-pass system allows the use of a microturbine which was heretofore not practical since the available temperature for powering the chiller fluctuated.
In the present invention, the purpose of the by-pass system for the recuperator is to flow the turbine exhaust into a heat exchanger or boiler and to divert the turbine exhaust when the heat exchanger is not in operation or is not required. To this end the turbine exhaust is directed directly into the recuperator rather than being directed into the heat exchanger. Obviously, when the temperatures of the working fluids that are in indirect heat exchange relation with each other are at or near parity, the ability to transfer heat is difficult and at best, inefficient. This system serves to increase the output temperature of the recuperator by utilizing the high temperature exhaust from the turbine. That is to say, that the higher temperature turbine exhaust fluid is utilized to boost the usable output temperature. Consequently, the available temperature of the fluid discharging from the recuperator is efficiently increased by virtue of this invention so that useable temperature required for heat transfer is attained.